Generally, in high-risk occupations, the personnel will work in groups of at least two. However, oftentimes these groups become separated and individuals are left to their own devices. In the case of firemen, this can often happen in smoke-filled buildings. Thus, all too frequently, a firemen may find himself in a smoke-filled building alone and unable to determine how to escape from danger. Such a delicate situation can be compounded by the fireman's air pack running low on air. Also, it is quite possible that the fireman has with him an injured companion or an injured victim of the fire. In such a case, while he may know the way to escape, he might not be able to escape with his injured companion or with the victim. In such cases, it is extremely important that the fireman have some means by which he can notify fellow firemen that he needs assistance.